SUMMARYIn the present paper, a quasi-analytic method for solving structural optimization problems has been developed by co-ordinated use of mathematical transformations, high-quality approximation and a twolevel approximation strategy. The method which has the advantages of both generality in applications and high eciency in computations is especially of bene®t to large practical design problems. Several typical examples of dierent sorts have been optimized to test its power. #